Browsing by Author "Kaya, O."

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Comparison of Contents of Sugars, Organic Acids and Free Amino Acids in Raisins Obtained From Gök Üzüm (Vitis Vinifera L.)
(Hohere Bundeslehranstalt und Bundesamt fur Wein- und Obstbau Klosterneuburg, 2023) Karakus, S.; Ates, F.; Keskin, N.; Turan, M.; Kaya, O.
Raisins are known as an important source of many bioactive compounds such as organic acids, free amino acids, and sugars. In this study, oak ash and potassium carbonate solutions applied before drying were compared for their effects on the Gök Üzüm raisin, more specifically, its contents of organic acids, free amino acids, and sugar profile. The total acidity quantified in the samples of raisin, ranged from 20.30 to 117.08 ng/µL DW for the potassium dipping solution, while values ranged from 17.98 to 164.72 ng/µL DW for the oak ash dipping solution. In samples from either dip solution, serine was predominant, followed by alanine, asparagine, glutamine, aspartate, sarcosine, glutamate, and leucine, whereas gly-cine, arginine, proline, histidine, and valine were found to be the lowest amino acids. In the samples examined, fructose was the most abundant sugar, whereas the lowest sugars in raisins were xylose for oak ash application and galactose for potassium carbonate application. There was wide variation in the sugar profiles for both variants, with values ranging from 3043.48 to 0.71 g/100 g DW. Drying Gök Üzüm grapes after the treatment of oak ash dipping solution promotes a higher content of organic acids, amino acids and sugars as compared to drying after potassium carbonate solution treatments. These results could be used for the development of an attractive pre-drying solution in further studies for the production of both, raisins and perhaps other dried fruits. © 2023, Hohere Bundeslehranstalt und Bundesamt fur Wein- und Obstbau Klosterneuburg. All rights reserved.
Melatonin Enhances Antioxidant Defense and Physiological Stability in Grapevine (Vitis Vinifera L.) Cultivars ‘Merlot’ and ‘Erciş’ Under UV-B Stress
(Tech Science Press, 2025) Yıldız, S.; Keskin, N.; Kunter, B.; Hatterman-Valenti, H.; Kaya, O.
Climate change-driven environmental stresses, particularly ultraviolet-B (UV-B) radiation, pose severe threats to grapevine (Vitis vinifera L.) productivity and physiological stability. This study investigated the protective role of melatonin in in vitro plantlets of two grapevine cultivars, ‘Merlot’ and ‘Erciş’, subjected to low (≈8.25 μW cm−2, 16 h) and high (≈33 μW cm−2, 4 h) UV-B exposure. Significant cultivar-specific responses were observed (p < 0.001). The ‘Erciş’ cultivar exhibited higher oxidative stress, with malondialdehyde (MDA) levels reaching 24.30 mmol g−1 FW in control plants compared with 14.91 ± 0.25 mmol g−1 FW in ‘Merlot’. Melatonin provided dose-dependent mitigation, reducing MDA to 12.68 in ‘Erciş’ and 8.52 ± 0.13 in ‘Merlot’ at 200 μmol L−1. Antioxidant enzyme activities increased significantly: superoxide dismutase rose from 0.02 ± 0.01 to 0.10 EU g−1 in ‘Erciş’ and to 0.13 EU g−1 in ‘Merlot’, catalase increased up to 0.08 in ‘Erciş’ and 0.16 in ‘Merlot’, while ascorbate peroxidase reached 1.06 ± 0.02 and 1.20 ± 0.03, respectively. Pigment traits also improved, with chlorophyll content increasing to 23.70 μg cm−2 in ‘Merlot’ and 22.66 μg cm−2 in ‘Erciş’, alongside enhanced nitrogen balance index values. Secondary metabolites were elevated, particularly total phenolic content (8.23 GAE 100 g−1 in ‘Erciş’ and 5.99 in ‘Merlot’) and antioxidant capacity (17.24 and 8.15 μmol TE g−1, respectively). Correlation analyses revealed strong positive associations between melatonin and antioxidant enzymes (r = 0.54–0.85), while principal component analysis explained 64.71% of total variance, separating cultivars and treatments clearly. Clustering patterns showed distinct grouping of enzymatic defenses, phenolic compounds, and pigments, reflecting coordinated protective mechanisms. Overall, melatonin application, especially at 200 μmol L−1, significantly enhanced enzymatic and non-enzymatic antioxidant defenses, stabilized photosynthetic pigments, and reduced oxidative damage, with stronger protective efficiency in ‘Merlot’. The research provided valuable insights for developing biotechnological approaches to enhance grape stress tolerance in the context of climate change challenges. © © 2025 The Authors.